1. Field of the Invention
The invention relates to an ultraviolet irradiation device which is used for ultraviolet radiation bonding of an article to be treated which is often subject to changes such as deformations, color changes due to heat and the like, or for curing of inks and the like, the above described article being defined as plastic, thermal paper, liquid crystal and the like. The invention relates especially to an ultraviolet irradiation device of the optical path division type, by which a good distribution of illuminance is obtained on the surface of the article to be treated which is irradiated with light and in which the average illuminance is high.
2. Description of Related Art
The device shown in FIG. 9 was proposed by the present inventor and another as an ultraviolet irradiation device which can treat an article (hereinafter called a "workpiece") which is often subject to deformations and color changes due to heat without using a cooling means. This drawing and a full description thereof can be found in commonly assigned, co-pending U.S. patent application Ser. No. 08/822,944, and as such, the "Prior Art" legend should not be viewed as an admission that this device is prior art with respect to this application within the meaning of the U.S. patent laws.
In FIG. 9, a cage-like body 10 of an ultraviolet irradiation device is shown within which a rod-shaped high pressure mercury lamp 11 is provided. Some of the light emitted from rod-shaped lamp 11 is incident upon a trough-shaped cold mirror 12, while the other part thereof is incident in plate-shaped cold mirrors 14, 15. Of the light which is incident upon the trough-shaped cold mirror 12, some of the visible radiation and infrared light is transmitted by the trough-shaped cold mirror 12, and the ultraviolet light (including some of the visible radiation and infrared light) is reflected by the trough-shaped cold mirror 12 and is incident upon the plate-shaped cold mirror 14. The light reflected thereby is incident upon a heat reflection filter 13 from which some of the visible radiation is reflected while the rest of the light is incident upon workpiece W.
On the other hand, of the light which was radiated by rod-shaped lamp 11 and which was incident directly in cold mirrors 14, 15, some of the visible radiation and infrared light is transmitted by cold mirrors 14, 15, while the ultraviolet light (including some of the visible radiation and infrared light) is reflected the plate-shaped cold mirrors 14, 15. The UV light reflected by plate-shaped cold mirrors 14, 15, furthermore, is incident in heat reflection filter 13, in which some of the visible radiation is reflected and the other light is incident on workpiece W.
By the measure that the reflection light from trough-shaped cold mirror 12 and the light projected directly by rod-shaped lamp 11 are reflected by cold mirrors 14, 15 and only the light reflected by the cold mirrors 14, 15 is radiated via heat reflection filter 13 onto workpiece W, the portions of infrared light and visible radiation can be relatively reduced and workpiece W can be irradiated with light which has a large proportion of ultraviolet radiation.
The above described ultraviolet irradiation device has the following shortcomings:
For effective use of the light from rod-shaped lamp 11, it is necessary for the light to be emitted parallel to cold mirror 14 or focused. The cross-sectional shape of trough-shaped cold mirror 12 is therefore oval or parabolic. The light reflected by the mirror with this cross-sectional shape has a distribution of the radiance on the irradiated surface which is in the form of a Gaussian distribution. The distribution of the radiance in the transverse direction of the rod-shaped lamp is therefore worse than the distribution of the radiance in the longitudinal direction.
In this poor distribution of radiance, and for a nonuniform distribution of the irradiance on the irradiated region, the following defects occur.
(a) Since in the irradiated area on the workpiece the treatment time is fixed based on the radiance at a minimum value, the workpiece treatment time becomes longer. In the case of a workpiece in which overcuring is not a problem, regardless of the radiance distribution, the treatment time can be reduced when the overall power is increased. But, it is necessary to increase the power supplied to the lamp, thus adversely affecting efficiency.
If the light power is not increased, the workpiece is treated within an irradiated region which has at least a certain radiance. However, the workpiece which can be treated must be made smaller.
(b) In the case of use, for example, for bonding a lens or for similar purposes, thermal distortion occurs due to the different absorption of UV radiation according to the locations where the bonding agent is applied, and stress-strain occurs due to a nonuniform curing reaction if the radiance distribution is nonuniform.
The correct above described defects, for example, the following measures can be considered:
(1) The distance between the lamp and irradiated surface of the workpiece is increased.
(2) The mirror and filter have a scattering function. For example, the surface/back of heat reflection filter 13 is sand blasted or slight dimpling or trough-shaped cold mirror 12 is provided, so that a formation like the surface of a golf ball is obtained. Or trough-shaped cold mirror 12/cold mirror 14 is formed as a polyhedron.
In case (1), the irradiance on the workpiece surface is reduced and the treatment time is lengthened. Furthermore, the entire system including the transport system, and thus the space occupied by the treatment device, becomes large.
In case (2), with sandblasting, the irradiance and thus the efficiency is reduced. Furthermore, for the slight dimpling or in the formation of a polyhedron, for light emergence with high efficiency and also to improve the irradiance, the construction of the form and the arrangement is difficult.